I can’t find the extension after installing it

This problem occurs when Magento can’t read the file app/etc/modules/NAME.xml (where NAME should relate to the module you just installed or the developer who created the module). If the newly installed extension is not listed under System > Configuration > Advanced > Disable Modules Output, try the following: 

• Ensure the uploaded files’ permissions can be read by Magento 
• Flush Magento’s cache and/or manually delete the contents of var/cache. In rare cases if var/cache is not writable by Magento, it will cache files in your system’s tmp/ folder